Matched tubes: sure?

[pulsar705]

How do I know if a quad-tube bought in a shop is matched really?
Can i to check something with a DMM or I have to blindly trust the seller ?
What can go wrong if i use unmatched tubes in my Peavey Classic 30 ?
I read that Electro Harmonics tubes do not fit the C30 because they are calibrated very "hot". What does this mean,it's true? If I decide to buy a quartet of EL84 for my C30, which features each tube should be,the plate current indicated on the package ?

I'm sorry for many questions

[bnwitt]

You have to blindly trust the seller.

Please be aware that matched tubes may not be matched in your amp. The real test is always in the amp. I use a Maximatcher to match tubes and many tube sellers use that device as well. This unit tests tubes at a max of 400 volts dc. Many amplifiers have plate and screen voltages that approach 500 VDC and when a set matched at 400VDC is put in that environment all bets are off.

That being said, the plate voltages in your amp are below 400 volts (in the range of 330VDC)and the Maximatcher tests EL84's at 325 volts. So, you should have no problems if you buy from a reputable seller who uses that device or any other quality unit.

However, your amp is not a typical cathode biased EL84 circuit, but rather is a non adjustable fixed bias setup. Because tubes vary in their conductance from unit to unit you may find a different sound from one matched set to the next. One set could pull close to max dissipation with your fixed -14VDC bias voltage, while another could run very cold and anemic. If that were my amp I would convert it to an adjustable fixed bias setup so I could dial in my tone/tube life set point.

[Enzo]

And let's point out that the manufacturers of the amps don;t bother with matching. Absolutely nothing will be harmed by mismatched tubes, other than certain tonal nuance. The amp will not suffer in the slightest electrically. Certaily all those decades, Leo Fender never wasted his money on matched tubes.

EH tubes could tend a little hotter than average overall, I don;t know anything about that, but it is possible. But they are not calibrated to anything. You can buy a ton of them and measure them and match them up if you like, and some will be hotter than others. But they are not "calibrated" any more than any other brand.

It is important that tubes have a reasonable bias, but it is nowhere near as critical as the general amp owner thinks it is. Bias is very much like the tire pressure in your car. It needs to be reasonable. The door of the car might say 32 pounds, but if they are at 34 pounds or 30, you car would still drive down the freeway with no trouble. The Peavey amp was designed to work reliably with just about any tube you might select. It is possible some particular set of tubes might be overly hot in your amp, but not really something to worrry about.

[bnwitt]

I completely agree with everything Enzo says. As long as the tubes aren't red plating you're fine. At -14VDC bias, most EL84 tubes will be well under max. That being said, tubes running too cold can sound like crap. So, I still recommend the adjustable bias mod for fine tuning tone with any set of tubes and for throttling down a particularly hot set tubes if you get them.

Mismatched power tubes have been part of some really great amp tone over the years too. Don't forget that a matched set of power tubes seldom remain matched over time.

[tubeswell]

FWIW I run unmatched EL84s in my Classic 30 all the time and it sounds fine. If there's a slight hum problem, just try experimenting with swapping the tubes around a bit (so that you end up with the least hum by having the least-unmatched tubes on opposite sides of the OT primary from each other. FYI, the way the C30 output tubes are wired in, the 'outer two' EL84 sockets are opposite each other and the 'inner two' sockets are opposite each other)

[pulsar705]

Originally Posted by tubeswell

FWIW I run unmatched EL84s in my Classic 30 all the time and it sounds fine.

Indeed, it would be absurd to replace 4 tubes if one of them fails.If it's like that,i don't care a damn !
And...if i want to do the bias mod, can I adjust it with amp on?

Thank you all

[bnwitt]

Originally Posted by pulsar705

And...if i want to do the bias mod, can I adjust it with amp on?

Thank you all

Well yes, you have to. You are setting idle current on the tubes and the amp has to be on with no signal (volumes at zero). You set the current to be below max (no red plating) and at the tone you like. Set it, turn up the volume and play your guitar, set it again, up volume again and play.....etc until you get your tone. I haven't been in one of those amps in awhile. Tubeswell how is the layout regarding pulling the mod off?

[tubeswell]

Originally Posted by bnwitt

Tubeswell how is the layout regarding pulling the mod off?

Everything about modding that amp is finickity. One weekend I had to pull it apart and put it back together 13 times while I was troubleshooting what eventually (as usual) turned out to be stress-cracked jumper leads between the boards.

Once you get the boards out, the mod itself is not that difficult, you just have to make sure you've cut the trace properly for the 1R resistor, drill some extra holes here and there. Things that don't fit on the outside of the board have to be stuck on the inside of the board etc. (See www.blueguitar.org). All strictly voids the warranty of course, and few techs will want to touch your amp with a barge-pole ever again. Once you've started down the road with mods, you're one sad nanny. (What does that make me? Is this too much information?)

[Enzo]

The C30 responds well to numerous modificatios, but it is about THE worst chassis to work in. Well, the 5150 Combo is made the4 same way, but at least it is larger.

[mac1amps]

It's nice to hear that I'm not the only one that thinks of all the "matched" tube criteria as just marketing BS. It drives me nuts when I hear/read about so many folks that really get "caught-up" in it.
On the other hand-When ONE tube of a "set" of power tubes fails (assuming this isn't a NEW set that just happened to have a "dud" in it), in MOST cases, the rest of that set is most likely worn-out (even though they haven't "failed" per say), and "should" be replaced with a fresh "set" (matched or otherwise). It's the equivalent to a set of [guitar] strings, that have lost all their "sparkle" and tone, but just haven't broke (yet).

[Enzo]

Well, when your set is a week old, I tend to doubt the others are worn out.